The invention relates generally to the treatment of exposed and developed strips of photosensitive material, especially photographic filmstrips, having a series of image areas.
More particularly, the invention relates to a method in which an exposed and developed strip of photosensitive material with a series of image areas is conveyed along a predetermined path for treatment. During travel along the path, the photosensitive material passes by a scanning station in order to determine the positions of the image areas. Scanning of the photosensitive material may, for example, be performed photoelectrically via a scanning slit which extends perpendicular to the direction of travel of the photosensitive material. A processing station is situated downstream of the scanning station and is spaced from the latter by a distance which at least equals the combined length of several image areas. At the processing station, an operation is performed on the photosensitive material at locations corresponding to the image areas. Movement of an image area from the scanning station to the processing station is controlled by measurement of the distance traveled by the photosensitive material.
The invention also relates to an apparatus for operating with an exposed and developed strip of photosensitive material having a series of image areas. The apparatus includes a mechanism for transporting the photosensitive material along a predetermined path and a scanning station at which the photosensitive material is scanned, e.g., photoelectrically via a scanning slit extending transversely of the direction of travel of the photosensitive material, as the photosensitive material moves along the path. A memory is provided for storing the measurements obtained at the scanning station in correlation to the longitudinal coordinates of the regions from which the respective measurements were derived. The apparatus further includes a processor for calculating the longitudinal coordinates of the image areas based on the measurements obtained from a section of the photosensitive material having several image areas. A processing station is disposed downstream of the scanning station by a distance at least equal to the combined length of several image areas and has means for performing an operation on the photosensitive material at locations corresponding to the image areas. The apparatus additionally includes a device for measuring the distance of travel of the photosensitive material and movement of an image area from the scanning station to the processing station is controlled using measurements derived from such device.
A method and an apparatus of the type outlined above are known from the West German Patent No. 27 05 097. To calculate the longitudinal coordinates of the image areas, the distance between detectable, respective leading and trailing edges of the image areas are taken as the "true image area length". This makes it possible to locate less readily detectable second edges of image areas having a first edge which is readily detectable.
In the apparatus of the West German Patent, the scanning location is not the same as the processing location where a notch is applied to the margin of the photosensitive material in order to position the image areas in a copier. The spacing between the scanning location and the processing location can be used with advantage to increase the accuracy with which the edges of the image areas are located. After initial detection of a transparency jump indicative of an image area edge, it is advantageous to examine an additional section of the photosensitive material in order to determine whether this transparency jump is not due to a vertical, poorly illuminated telegraph pole which causes a transparency jump similar to that of an image area edge. Recognition of the image area edges with an adequate degree of reliability is thus possible only after examination of an additional test section having a length at least equal to that of an image area. The reliability with which the image area edges can be detected is increased when a section of the photosensitive material containing several image areas, and especially when the entire strip of photosensitive material, is examined using the knowledge of image area length, i.e., the distance from the leading to the trailing edge of an image area, and the width of the bands separating neighboring image areas. However, this requires very precise monitoring of the distance traveled as the photosensitive material moves from the phoeoelectric scanning station or measuring station to the processing station. Measurement of the distance traveled is normally accomplished by converting the rotational motion of friction rolls which engage the photosensitive material into pulses or by means of a counter for the pulses delivered to a stepping motor constituting part of the drive mechanism for the photosensitive material. For the measurement to be accurate, no slip should occur between the measuring rolls and the surface of the photosensitive material, and the measuring rolls, which are caused to rotate by friction, should not undergo changes in diameter due to wear. These two requirements are very difficult to satisfy simultaneously. As a rule, rolls having a high coefficient of friction are subject to wear and can also deform elastically. Wear-resistant rolls, on the other hand, have a smooth surface so that slip occurs readily. Furthermore, the pressure of the measuring or drive rolls cannot be increased arbitrarily since the photosensitive material can then be damaged Inasmuch as errors in measurement add up, precision in following movement of the photosensitive material is critical, particularly when the distance to be traveled by the photosensitive material is large.